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<h1>The Sound Board</h1>

<h2>Dome Construction</h2>

<p>The sound board is domed a few millimeters. The dome improves its ability to withstand stress caused by humidity changes: In times of high moisture, the board can expand, in times of low humidity, the board can contract.</p>

<p>Expansion and contraction appears more across the grain than lengthwise, according to the properties of the wood. This means that the board width changes more than the length.</p>

<p>Changes in board dimensions will change the dome height. This effect can be observed as string clearance change at the 12th fret.</p>

<p>As a consequence, the room climate (temperature, and more important, humidity) must be carefully controlled during construnction in the workshop. A relative humidity of 40% is advisable. Less is not so problematic, but more than 60 is.</p>

<p>To create the dome, bars and braces are glued on while the soundboard lies on an arched workboard, the solera. Clamping pressure forces the soundboard into the domed shape of the solera. The shape of the soundboard dome is not so much important, and also not precisely controllable: When the glue clamps are removed, the springback force of the whole arrangement will flatten the shape a little bit. Furthermore, when the braces are shaped and thinned, the dome shape and height also changes somewhat.</p>

<p>As a result, every sound board has its own individual geometry. Specifically, the dome height at bridge position cannot be predicted precisely. As a consequence, neck angle and fretboard thickness may have to be adjusted to the particular sound board geometry.</p>

<p>As already mentioned, the exact shape of the dome is not so important. Some builders argue to have the solera scooped out to the shape of a sphere, because then they could use a radius sanding disk to sand the sides down to the proper contact angle that the soundboard dictates. But because of the unpredictable springback effects, this method does not guarantee exact results. Not only that a giant radius disk requires considerable amount of effort to build, space to store, and preparation with stick-on sandpaper, patient eyeballing and a simple sanding stick will likely give similar, if not better results when it comes to preparing the side for glueing to the top.</p>

<p>There are 3 ways to create the dome:</p>

<ul>
<li>Contour the underside of struts and braces before glueing, and clamp them against the sound board.</li>
<li>Use a dished workboard, clamp straight struts and braces against soundboard and workboard</li>
<li>Combination of both</li>
</ul>

<p>Contouring can be achieved in multiple ways: hot bending, arching and sanding the convex head flat, sanding with a radius stick, etc.</p>

<p>While the first method allows a jump-start guitar-building, the use of a dished solera is a useful investment if you plan to build more than a single guitar. The solera guarantees repeatable results (within the limits), allows to clamp multiple braces at once, and facilitates experimenting with different bracing patterns.</p>

<p>Preshaping of braces is easy with a dished solera: Just place a piece of sandpaper on the solera, and rub the brace over it. The brace will take the shape of the solera surface.</p>

<p>If the braces are not shaped before glueing, the solera will have to be scooped out more exagerated, because the assembly spring-back effect will be larger.</p>

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